In "Baby . . .Secret of the Lost Legend," Susan Loomis (Sean Young) is an archeologist looking for fossils in equatorial West Africa; her boss, Dr. Eric Kiviat (Patrick McGoohan), is a fossil looking for a living dinosaur known to the natives as "Mokele-Mobembe." Her husband George (William Katt) is a sportswriter who has taken a leave to be with his wife -- Tarzan swinging on an apron string.

George wants to return to the States, take a job with The Washington Post and make babies; Susan wants a "find" to establish her career. Both get what they want when they beat Kiviat to the punch, discovering and adopting the baby of "Baby," a hippo-sized brontosaurus hatchling. Re-enter the evil Dr. Kiviat, who kills Bronto-dad, captures Bronto-mom, and heads upstream.

What follows is a yabba-dabba-dubious adventure plot, notable only for the racist ridicule of the Africans involved, and a lot of cutesy stuff that has less to do with Dr. Jane Goodall than Dr. Leo Buscaglia. Baby wears George's underwear on its snout; Baby interrupts the young couple in the act of love; Baby enters the tent to sleep with the folks -- tent collapses. All of which is Susan's cue to say, "Awwww, Baaaaay-beeeeee!" and offer a hug.

Most of the budget of "Baby" seems to have gone into the creatures, who nevertheless don't look much better than Gumby. The comedy centers on poor, beleaguered George as he is stung by bees or decked by Baby's tail; poor, beleagured Katt looks as if he's being strangled by his own mannerisms.

Mired in all of this is the beautifully tawny, thin-limbed Sean Young, playing every Princeton coed you ever wanted to invite upstairs to hear you recite your poetry. Darn that PG rating! Here in Africa, Young makes you yearn for the cheesecake-on-safari of "Sheena." Bring on the Veldtveeta! Baby . . . Secret of the Lost Legend is rated PG.